1. Field of the Invention
The present invention relates to a wiring structure for an automobile multiplex communication system.
2. Description of the Related Art
In recent years, there have been developed automobile multiplex communication systems in which a plurality of control units each comprising a microcomputer or the like are installed on an automobile body for multiplex communications between those control units.
As shown in FIG. 3 of the accompanying drawings, a conventional automobile multiplex communication system includes a plurality of control units (ECUs) "a" interconnected by communication signal lines "b" in the form of twisted pairs which are connected to circuits "d" including microcomputers in the ECUs "a" through connectors "c" such as multiterminal connectors or the like.
Since automobiles are subject to external noise, the communication signal lines "b" are covered with shield wires "e" between the ECUs "a" for preventing the communication signal lines "b" from being affected by such external noise.
The shield wires "e" are required to be grounded to a location which is not susceptible to external noise, e.g., a conductor of the automobile body. Heretofore, the shield wires "e" have been grounded as follows:
As with the communication signal lines "b", the ends of the shield wires "e" which cover the communication signal lines "b" between the ECUs "a" are introduced into the ECUs "a" through the connectors "c". In the ECU "a" in which plural communication signal lines "b" and shield wires "e" are introduced, i.e., in the central ECU "a" shown in FIG. 3, the communication signal lines "b" are connected to each other, and the shield wires "e" are connected to each other. With respect to one of the ECUs "a", i.e., with respect to the central ECU "a" shown in FIG. 3, the shield wires "e" introduced through the connector "c" into the ECU "a" are led out of the ECU "a" and grounded to a conductor "f" of the automobile body.
The above wiring structure for the automobile multiplex communication system suffers the following drawbacks:
The portions of the communication signal lines "b" which are covered by the shield wires "e" between the ECUs "a" are protected against entry of external noise into the communication signal lines "b". However, since the connector terminals of the connectors "c" which are connected to the communication signal lines "b" tend to be not fully shielded, external noise applied to the shield wires "e" is likely to be picked up by the shield wires "e" serving as an antenna and applied through the connector terminals to the communication signal lines "b". Consequently, it has been impossible to sufficiently protect the automobile multiplex communication system against entry of external noise into the communication signal lines "b".